1. Field of the Invention
The present invention relates to an acoustic diaphragm and a speaker using the acoustic diaphragm.
2. Description of the Related Art
Digital audio contents with high sound quality, such as those in an audio DVD, a super audio CD (SACD) and the like, have emerged, whereby a speaker system capable of thoroughly reproducing the quality intrinsic to the contents is desired to be developed.
As a material of a diaphragm mounted on such a speaker system, a uniform material such as uniform paper, plastics, metal is widely used.
However, in a case of using the uniform material as the material of the diaphragm, a sound propagation speed is equalized in every direction, and accordingly, in some case, a standing wave is prone to occur, and sound field expression becomes poor.
As a diaphragm that enriches the sound field expression, for example, a diaphragm of the oblique cone type is known. The diaphragm of the oblique cone type is a diaphragm in which a cross-sectional shape is, made asymmetric by shifting a position of a voice coil from a center of the diaphragm. By making the cross-sectional shape asymmetric, resonance is dispersed, thus making it possible to reduce a peak that appears in treble characteristics. Accordingly, a more natural reproduced sound can be obtained.
However, since the diaphragm of the oblique cone type has a more complicated shape than a general diaphragm, it is difficult to manufacture the diaphragm of the oblique cone type. Moreover, since the diaphragm of the oblique cone type has a bias in directivity, there is also one that is rather less likely to emit a sound forward. Furthermore, in the case of using the diaphragm of the oblique cone type, there is a case where improvement of characteristics of a bass sound is not sufficient though characteristics of middle and treble sounds are improved.
Meanwhile, as another diaphragm that enriches the sound field expression, a diaphragm of the wood cone type, which uses natural wood, is also known. In the diaphragm of the wood cone type, the sound propagation speed differs between a fiber direction and directions other than the fiber direction, and accordingly, the standing wave does not occur, and good sound field expression and bass energy are also brought. The diaphragm of the wood cone type is described, for example, in Japanese Unexamined Patent Application Laid-Open (Koukai) No. 2004-254013.
An acoustic diaphragm and a speaker are desired to emerge, which can enrich the sound field expression and have excellent reproduction characteristics of the bass sound in both the case of using the uniform material as the diaphragm and the case of using the natural wood (wood sheet) as the diaphragm.